How to find ADFS Reference Number errors

ADFS error reference numbers displayed on the adfs login page (see below) can be found in the Windows Server logs.

Open the Server Event Viewer.
Navigate to Applications and Services Logs > AD FS 2.0 > Admin.
Select 'View' from the main menu > Add/Remove Columns... > add the "Correlation Id" column.

You can now look up the reference number in the "Correlation Id" column.